HP StorageWorks XP24000 Continuous Access Software User and Reference Guide, v01 (T5278-96002, June 2007)

Host Failover So
ftware
Host failover soft ware, which transfers information between host servers at the primar y and remote sites,
is a
critical component of any disaster recovery effort. Host failover is confi gured using the desired host
failover software product for the platform (for example, Microsoft Cluster Server), depending on your
installation r
equirements and standards. The storage system program products do not provide any
host failover
functions.
When Continuous Access is used as a data migration tool, host failover is recommended but not required.
When
Continuous Access is used as a disaster recovery tool, host failover is required to ensu re effective
disaster recovery operations. When a Continuous Access pair is suspended due to an error condition,
the
MCU gener
ates sense information which should b e transferred to the remote s ite via the host failover
software for
effective disaster detection and recovery.
Continuous Access Remote Copy Operations
Figure 2 on page 18 illustrates the two types of Continuous Access remote copy operations: initial copy
and update copy. To reduce the overhead associated with these remote copy activities and maximize
data transfer, the storage system utilizes a special write command which is allowed only for Continuous
Access initial and update copy operations. This command transfers the control parameters and the
FBA-format data for consecutive updated records in a track using a single write operation. The special
Continuous Access write command elim inates the overhead required for performing FBA-to-CKD and
CKD-to-FBA conversions.
Figure 2 Remote C opy Operations
This section describes the following aspects of Continuous Access remote copy operations:
•
Initial copy operations (see “Initial Copy Operation” on page 18)
•
Update copy operations (see “Update Copy Operation” on page 19)
• Read and write I/O operations for Continuous Access Volumes (see
“Read and Write I/O Operations for Continuous Access Volumes”onpage19)
•
S-VOL write option (see “S-VOL Write Op tion” on page 20)
•
Difference managem ent (see “Difference Managem ent” on page 20)
Initial Copy Operation
The initial copy operation synchro nizes the P-VOL and S-VOL independently of host I/O processes.
The initial copy operation is the same for Continuous Access Synchronous and Continuous Access
Asynchronous pairs. A Continuous Access initial copy operation takes p lace when you a dd a pair
(paircreate) or resynchronize a split/suspended pair (pairresync). When a new pair is created, the entire
contents of the P-VOL is copied to the S -VOL cylinder by track, except for the diagnostic and unassigned
alternate tracks. You can also select None for the initial copy mode. If None is selected, the user is
responsible for ensuring that the P-VOL and S-VOL are already identical. The MCU cannot verify the
contents of the volumes. When a split/suspended pair is resynchronized (pairresyn c), only cylinder #0
and out-of-sync tracks (updated by write I/Os during split/suspend) are copied to the S-VOL.
Note: For further information on cylinder/track difference m anagement, see
“Difference Management” on page 20.
18
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HP StorageWorks XP Continuous Access Software Operations